Changes

==Navigation==

==Navigation==

It is essential that the precise location of the survey be known, and this is where navigation is important. The work horse of the industry, certainly in the Gulf of Mexico, is the shore-based navigation system ''Syledis''. In the Gulf and in other areas, base stations have been placed on production platforms to extend the range of coverage. Another system, Star-Fix, uses commercial satellites and a shore-based network of stations to determine the position of the satellites precisely. Given this information, the position of the vessel can be calculated. Another satellite system is the Global Positioning System (GPS), which is now being installed by the U.S. government. It is still unclear whether its capabilities will be intentionally degraded for commercial applications. GPS (or differential GPS) has the potential to make all other navigation systems obsolete.

It is essential that the precise location of the survey be known, and this is where navigation is important. The work horse of the industry, certainly in the [[Gulf of Mexico]], is the shore-based navigation system ''Syledis''. In the Gulf and in other areas, base stations have been placed on production platforms to extend the range of coverage. Another system, Star-Fix, uses commercial satellites and a shore-based network of stations to determine the position of the satellites precisely. Given this information, the position of the vessel can be calculated. Another satellite system is the Global Positioning System (GPS), which is now being installed by the U.S. government. It is still unclear whether its capabilities will be intentionally degraded for commercial applications. GPS (or differential GPS) has the potential to make all other navigation systems obsolete.

The advent of 3-D seismic has increased the demand for accuracy in positioning. One needs to know within a few meters the position of the source and the position of each detector group for every seismic shot. Underwater, acoustical systems and/or laser measurement through the air are used to determine the positions of things in the water near the vessel. Extremely accurate magnetic compasses are attached along the streamer cable, and sometimes a navigation receiver is placed in the tail buoy at the end of the streamer cable. Accuracies of a few meters are desirable.

The advent of 3-D seismic has increased the demand for accuracy in positioning. One needs to know within a few meters the position of the source and the position of each detector group for every seismic shot. Underwater, acoustical systems and/or laser measurement through the air are used to determine the positions of things in the water near the vessel. Extremely accurate magnetic compasses are attached along the streamer cable, and sometimes a navigation receiver is placed in the tail buoy at the end of the streamer cable. Accuracies of a few meters are desirable.